The present invention relates to the field of digital computers and specifically to methods and apparatus whereby the states of latch circuits or other points within a data processing system are accessed for the purpose of fault detection, fault analysis, maintainance and other tasks.
In high-speed, large-scale data processing systems, the ability to detect the state of any latch or other circuit within the data processing system is desirable in order to be able to detect and analyze fault conditions. Prior art systems have frequently direct-wired key points in the data processing system to a control panel or console to illuminate the console lamps and to thereby give an indication of the status of storage circuits within the system. The direct-wired approach, however, becomes unwieldy for large data processing systems because the number of illuminating lamps on the system console becomes too large for useful or convenient operator analysis.
Other prior art systems have employed the computing capability of the data processig system itself to log-out data indicating the state of circuits. In order to log-out data, the conventional data paths of the data processing system are employed to store the logged-out data in prescribed locations of system storage. Such a use of the conventional data paths in the data processing system has the problem that, if the data paths or control circuitry associated therewith are faulty, the information logged out is in error so that fault location becomes both difficult and time-consuming.
In order to overcome these problems, the above cross-referenced application entitled DATA PROCESSING SYSTEM AND INFORMATION SCAN OUT provided an improved system for fault detection and analysis. The data processing system disclosed in that application includes a primary apparatus for carrying out principal instruction-controlled data manipulations and includes a secondary apparatus for independently addressing storage locations and other points within the principal apparatus. The secondary apparatus includes an instruction-controlled digital couter which has the capability of accessing information from the primary apparatus and the capability of analyzing the accessed information to identify faults or to carry out other tasks. In that cross-referenced system, the primary apparatus is typically a large-scaled data processing system, such as the AMDAHL 470V/6 system.
The identification of faults in the data processing system of the above cross-referenced application, or more generally in any system, requires the comparison of expected values of information with actual values of information. The presence of differences between expected and actual values indicates that a fault has occurred. The points causing the difference are used to identify the fault. In order to increase the probability of detecting a fault, it is desirable to check a large number of points in the system. In a large-scale data processing system, a comparison of thousands of points are typically required for adequate fault detection and analysis. Furthermore, the address space used to specify the points is usually even much larger than the number of points actually used for fault detection or analysis. The greater the number of points to be compared, however, the more time-consuming are the comparisons and the larger the data base of expected values required. A greater time consumption to detect faults is, of course, undesirable in that such greater time detracts from the efficiency of the data processing system and its availability for more useful tasks. Also, the requirement for a larger data base is undesirable since it requires more storage to store the data base.
While the above cross-referenced application discloses significant improvement in fault detection and analysis, problems still exist when large numbers of points must be examined for fault detection. A need exists for improved methods and apparatus for detecting faults for a large number of points in a data processing system.